Method of bonding fused crystalline alumina.



UNITED STATES PATENT OFFICE.

THOMAS B. ALLEN, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO THE CARBORUN-DUM COMPANY, OF NIAGARA FALLS, NEW YORK, A CORPORATION OF PENNSYL-VANIA.

1,107,011, Specification of Letters Patent.

N 0 Drawing. Application filed March 11, 1913.

' Patented Aug. 11, 1914.

Serial No. 753,648.

17 b all whom it may concern:

ie it known that I, THOMAS B. ALLEN, a subject of the King of GreatBritain, residing at Niagara Falls, Niagara county, New York, haveinvented a new and useful Method of Bonding Fused Crystalline Alumina,of which the following is a full, clear, and exact description.

My invention relates to the manufacture of refractory articles formed ofgrains of fused crystalline alumina held together by a binder.

The object of the invention is to provide a simple and efiicient processfor this purpose, which may be used at temperatures below those wherealumina softens.

My method consists in forming on the surface of the grain and partlyfrom its substance a highly refractory aluminum compound, such asaluminum borate or aluminum borid.

In carrying out my invention I preferably mix the grains of aluminaintimately with a small quantity of a solution of boric acid andglycerin. The quantity .of this solution need not exceed five per cent.of the total mix, and is preferably prepared by heatingabout eightyparts of glycerin and dissolving therein about twenty parts of finelypowdered boric'acid. This mixture of alu mina grains, boric acid andglycerin, which is preferably about the constituency of moldingsand, isthen molded into the desired shape in any suitable way, as by pressingor tamping. The articles thus formed are then fired in a pottery kiln toa temperature of about 1350 degrees or above. During this firing some ofthe boric acid is lost by volatilization, but a portion combines withthe surface of the grains, bonding them together very firmly but stillleaving the article very porous This article is substantially asrefractory in character as if composed of alumina alone.

The advantages of my invention will be apparent to those skilled in theart, since the process can be carried out at ordinary kiln temperatures,and does not require the higher range of temperatures near the softeningpoint of alumina. The articles have great tensile strength, and aresubstantially as refractory as the. fused alumina of which they arecomposed. They are also very porous, being capable of absorbing about 18per cent. of their own weight of water. The glycerin solution is ofespecial advantage in obtaining the bonding action at the desiredtemperature; for I find that aqueous solutions of boric acid do notexert this' bonding action at temperatures commonly obtained in potterykilns. I have also been unable to bond articles by mixing powdered boricacid and water with the alumina and heating to a temperature of 1350degrees C. The glycerin solution of other acids may be used, such asthat of phosphoric acid. This gives a satisfactory bond, but not quiteas strong as the boric acid bond. The solution of boric acid andglycerin prepared as herein described forms a product known chemicallyas glycero-boric acid. The method may also be applied to the makingof'articles of fuzed alumina for abrasive, mechanical, electrical, andother purposes. Alumina grains of any degree of fineness may be used,from No. 16 mesh down to the finest powders. I have found that forgeneral refractory purposes grains sized to 150 mesh will give a strongand durable article when treated by my process.

By the words consisting essentially of in my claims, I mean that atleast the major part of the article is alumina.

I claim:

1. The method of bonding molded articles consisting essentially ofalumina, which consists in molding a mixture of alumina and a glycerinsolution of an acid, the acid radical of which is capable of unitingwith alumina, and heating the article to a temperature where suchreaction will take place.

2. The method of bonding molded articles consisting essentially ofalumina, which consists in molding a mixture of alumina and a glycerinsolution of an acid, the acid radical of which is capable of unitingwith alumina, and heating the article to a temperaturejof at least 1300degrees C. or above. 3. The method of bonding molded articles consistingessentially of alumina, which consists in molding a mixture of. alumina,boric acid and glycerin, and firing the articles to a temperaturesuificient to cause the boric acid to combine with the alumina and bondthe article.

. 105. 4. The method of bonding molded articles In testimony whereof, Ihave hereunto set my hand.

THOS. B. ALLEN.

Witnesses:

ARTHUR Burrs, J. M. MANL Y.

